1. Field of the Invention
This invention lies in the field of seismic field operations. More particularly, it concerns an improved cable construction in which the cables are made in multiple separate units, each provided with a connector plug by means of which they can be connected in series. Each of these separate cable elements or segments has a plurality of take-outs. The electrical signals from these multiple take-outs are multiplexed in the connector plugs so that a number P of separate geophone groups, connected one to each of the take-outs can be multiplexed and transmitted to the recording truck on a single conductor pair. By this means, the total number of connector pairs in the cable can be reduced by a factor of approximately P-1.
2. Description of the Prior Art
In the prior art there are two basic systems of handling the geophone signals between the geophones and the central recording unit or recording truck. The most common method is to provide a multiconductor cable which may be in one long unit, or it can be made from a plurality of cable segments, each of which are connected together in series to provide the desired length of cable. In the conventional system, if there are a total of T geophone groups to be connected to the recording truck, it will require, as a minimum, T conductor pairs in each of the segments of the cable. In view of the high multiplicity of recording channels being utilized in seismic field operations, this requires a very heavy and costly cable to connect each of the geophone groups independently to the recording truck.
In the second type of data acquisitions system a group of array terminals are provided into each of which a group of geophone leads can be attached. These may be from one to any desired number, such as 16, for example. In the array terminal the individual geophone signals are digitized and sequentially transmitted from the array terminal, over a two conductor high frequency digital transmission channel, to the next array terminal, and through that array terminal, to the next one, and the next one, and so on, until it reaches the recording truck. While this can handle immense numbers of recording channels, it is a very expensive and, to say the least, not trouble-free system of data acquisition. The subject of this invention lies in the area between the group 1 system and the group 2 system just described.